1. Field of the Invention
This invention relates to a voltage controlled variable gain amplifier circuit that varies its gain linearly against a gain control voltage.
2. Description of the Related Art
There have been known a programmable gain amplifier circuit that discretely varies its gain against the gain control voltage and a voltage controlled variable gain amplifier circuit that linearly varies a logarithm of its gain against the gain control voltage. Depending on application fields of the voltage controlled variable gain amplifier circuit, however, developing a voltage controlled variable gain amplifier circuit that varies its gain linearly and continuously against the gain control voltage is required in order to improve controllability of the gain. Related technologies are disclosed in Japanese Patent Application Publication No. H05-218767, for example.
This invention is directed to providing a voltage controlled variable gain amplifier circuit that varies its gain linearly and continuously against the gain control voltage. Also, this invention is directed to suppressing dependence of the gain of the voltage controlled variable gain amplifier circuit on a power supply voltage.
Furthermore, this invention is directed to suppressing variations due to semiconductor manufacturing processes and temperature dependence of the gain of the voltage controlled variable gain amplifier circuit.